Milk is a significant foodstuff both as a starting material in numerous products and as a final product. An important part of milk production, is to ensure that the milk is of good quality and, specifically, free from bacteria and other pathogens or contaminants that could have a bearing on its quality. When a diary animal suffers from an infection of the udder, the first outward sign is often a change in the milk. Specifically, milk may contain small quantities of blood, puss or other contaminants that change the colour of the milk. Many national and international regulations stipulate that any such milk be separated and not used for human consumption. In automated milking systems in which teat cups are connected automatically to the teats of an animal, a visual inspection of the milk is impractical, but the need for quality verification and possible separation of milk is of paramount importance to prevent sub-standard milk from being mixed with milk from healthy animals to the detriment of the bulk milk quality.
DE 27 59 126 describes an arrangement for separating milk which includes a light source and photodiode for detecting the colour of milk. When the colour of the milk indicates that it contains blood and puss, the milk is diverted to a separate container. This system, while it may permit some degree of colour change to be determined, cannot provide any great accuracy and consequently caries the risk of sub-standard milk being mixed with bulk milk or good milk being discarded.
WO 98/30084 describes an automatic milking arrangement that is equipped with a colour sensing system that is sensitive to frequency bands for red, green and blue light. The intensity signals from each colour band are compared mutually and with reference values to determine a change in colour. The reference values may be an average of recently determined values for each animal at a number of previous milking runs or a common value obtained from the milk of all animals. While this system enables a change of colour to be determined more accurately by virtue of the different colours detected, it nevertheless requires careful calibration to maintain this accuracy and to compensate for changes in temperature and aging of the various components, which ultimately makes it difficult to use reliably in practice.
It is an object of the present to overcome the problems of the prior art and provide a sensor arrangement that can detect a colour change indicative of the presence of certain contaminants in milk, milk products and other fluids and that is inherently accurate and reliable over time.